Navigation computer



Feb. 16, 1943. 1', L THURLQW El-AL 2,311,005

NAVIGATION COMPUTER Filed July 3l, 1940 2 sheets-sheet 1 NEEM;

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NAVIGATION (')OIJHFU'IER` 'Filed July 31, 1940 2 sheets-sheet 2 5a I4@ 8a a l l a "0' Mmmm: 6 1 3 12n- |90' |74, n'o, :g sla. 20o. 42u. low

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6M z m Q 'i5 Qld E8 y /Nl/e/vroks THOMAS A TH c//QL o rr SAMc/@L M. 50e/04 Patented Feb. 16,

OFFICE 2,311,005 NAVIGATION COMUTER Thomas 1i. Thurlow and Samuel M. Bur-ka, Dayton, Ohio Application July 31, 194o,\'seria1 No. 348,968

(crass- 61) (Granted under the act of March 3, 1883, as

1 Claim.

amended April 30, 1928; 370

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us-of any royalty thereon.

` This device primarily relates to an apparatus for computing longitude, when Greenwich civil time and local sidereal time are known. The apparatus may also be used to compute'local sidereal time, knowing longitude' and Greenwich civil time.

A secondary feature is the combination of the device with a telescope-training and driving mechanism in such a manner that the telescope may be trained on different celestial bodies without disturbing` the continuous operation of the driving mechanism and the time-indicating mechanism. In the navigation of aircraft'it has lbecome -it will known to x the position @fm1- Craft by meansbf'i new and -novel apparatus illustrated in this inprecomputed lines `of position used in conjunction with observations on celestial bodies. One

such systemis simultaneous altitude observations on two stars used in conjunction with a form of precbmputed lines of position printed in a book on Star Altitude Curves, United States Army Air Corps, published by Weems System of Navigation, Annapolis, Md.

Simultaneous altitude observations of two stars having been made, the latitude and local sidereal time of the observation position are obtainable from the intersection of lines of position of the two stars in the Star Altitude Curves book, latitude being readable as the ordinate, and local siderealvtime as the` abscissa. After the navigator has. obtained Greenwich civil time from a chronometer, and local sidereal time from sidereal time` and transforming the difference into units of arc readable as longitude.

It is a further object of this invention to provide, in connection with the sidereal-time-'indicating device, an indicating device. operatively associated therewith for computing and indicating the correction-to an altitude observation on Polaris for the particulartime in question, to thereby obtain the correct-latitude of observation position.

It is a further object of this invention to combine this device with a telescope having a constant speed motor and a training mechanism, so that the telescope will follow the celestial body upon which it is trained while it is in the field of view. In adapting the mechanism, the longitude-indicating mechanism is changed so that indicateright ascension. l By means of the vention, it is possible to change the position of the telescopefrom one celestial body to another without disconnecting the constant speed motor "and, consequently, without disrupting the continuous operation of the driving mechanism and the Star. Altitude Curves, it is necessary to mathematically convert Greenwich civil time to sidereal, time for a given longitude, obtain the algebraic difference Ybetween-local sidereal time and the sidereal time of the given longitude for the time of the observation, and convert the dii'- ference into longitude in units of arc. It is es. sential' that these latter vcalculations be made rapidly and accurately, especially when xing the position of a fast moving airplane.- It is for that Purpose that the devised.

It is, therefore,` an object oi' this invention to providea device for converting Greenwich civil time into sidereal time and obtaining the lon-vv present calculator has been gitude of the position of observation' by simultaneously obtaining the algebraic difference between the local s idereal time and'Greenwich ,ample only and are not to the. continuity of indication of sidereal time.

Other objects and advantages of this vinvention will become apparent from the following description taken in connection with the accompanying drawings, it being clearly understood that the same are by way of illustration and exway limiting the spirit or scope of this invention. The spirit and scope of this invention is to be limitedy only by the prior art and by the terms of the appended claims.

Referring to the drawings:

Figure 1 is a diagrammatic showing of a calculator in accordance with the invention; and

.Figure 2. is a diagrammatic showing of an adaptation of the calculator device.

Referring to the drawings, Figure 1, there are shown three counter mechanisms of the well-known Veeder type. Counter I indicates Greenwich civil time in hours, minutes, and seconds for any particular'indicated day. Counter 2 indicates sidereal time, either Greenwich or local, in hours, minutes, and seconds for a particular indicated day. Counter 3 indicates longitude-in units of degrees, minutes, and seconds. v

Counter I is operated by manually operable handle or input means 4 in conjunction with shaft 5 having gear 6 integral therewith. Gear 6 drivingly engages gear 8. which in turn operates the counter mechabe taken as in'any f and lparticularly to,

1, integral with shaft almanac.

; clutch'V shaft 8 from shaft I3 and, consequently, shaft 32. Upon further operation of handle 4,

nism l. Integral with shaft 8 is a clutch element 3. with which clutch element Il is adapted to be moved'into operative engagement by lever II, pivotally' mounted at I2 and having a collar II' pivotally attached thereto. Element III is free to rotate in collar II', but relative longitudinal movement between element Il and collar IIi is limited. Element I8 is attached to shaft I3 by a connection comprising va pin l2 integral with shaft I3V received in a slot 43 in member I0. Member I is thus connected to rotate with shaft 'I 3 and to move longitudinally with respect thereto. Shaft I3 has integral therewith a gear I4, adapted to mesh with gear I integral with shaft I3. Gear I'I, also integral with shaft IG, meshes with gear I8. Gear I8 is integral with one end of shaft I9, the other end of shaft I8 being provided with a pinion gear 22 forming a part of a differential gearing. Shaft I8 is freely ro tatable with respect to gear 28 and diierential housing 2l, which in turn is integral with gear 20. Gears 2l and 25, freely rotatably mounted in housing 2I, are adapted to mesh with gears 22 and 23. Gear 23 is integral with shaft 26, which in turn is freely rotatably received in housing 2 I. Shaft 26, adapted to be manually operated by handle or input means 28, has integral therewith agear 21 adapted to mesh with gear 29 integral with shaft 38, which in turn is operatively connected to counter mechanism 3. Gear 20 of the dierential mechanism is adapted to mesh with gear 3|, integral with shaft 32, which in turn is operatively connected to counter mechanism 2. The gearing system connecting shaft I3 to shaft 32 is selected as having a ratio which will convert civil time to sidereal time, differing from the ratio of the civil to the sidereal time by only two parts in ten million. The discrepancy in the above-stated ratios is equivalent to only six and one-third seconds of time, or ninety-five seconds of arc error, during the solar year. This system of gearing is disclosed in an article by A. E. Flanigan, entitled Gear Ratios for the Conversion of Civil to Sidereal Time, published in Review of Scientific Instruments, October,

1934. The gearing system connecting shaft 32 to shaft 30 is such `as to convert time units into units of arc, one hour of time being equivalent to fifteen degrees of arc.

In the operation of the device, the proper relationship between the civil and the sidereal time counters for the particular day of the observation is established by operation of handle l, with counter 3 set at zero longitude and with the clutch in operativo engagement, until the sidereal time count-er 2 indicates the. sidereal time of zero hours Greenwich 'civil time for the day of the observation, as obtained from the nautical Handle II is then operated to deshaft 8 is rotated to set counter I at zero. Naturally, this adjustment need not he made if handle 4 is turned an amount to correspond to the total lapse of time since the device was last used. However, if lche device has not been used for several days or more, it has been found to be more convenient to corelate civil and sidereal time bythe above-described method.v

With the shafts 8 and I3 operatively connected by the clutch, handle l is operated until counter I indicates Greenwich civil time as obtained from a chronometer. This civil time is converted into sidereal time by the connecting gearing, counter '3 being at zero. Since shaft 26 Vis stationary,

shaft 'I8 rotates gear 28'by means of gears 2l and and housing 2l which is integral' with gear 20. The altitudes of Aat least two stars are obtained by simultaneous, or substantially simultaneous, observances thereon; and with the aid of the Star Altitude Curves, the local sidereal time and the latitude of the position of observation are obtained. Since the algebraic dierence between local 'sidereal time as obtained from the Star Altitude Curves, and sidereal time as. .set on counter 2, is a. measure of the longitude of the position of observation in units of time, operation of handle 23 to set the reading of the local sidereal time on counter mechanism 2 will thereby result in an indication of the longitude on counter 3 in units of are. Since shaft I9 is stationary while operating handle 28, shaft 28 and gear 23 will cause simultaneous operation ofl counters 2 and 3 in a ratio relation of time to longitude in units of arc.

The device is also provided with operatively connected with the sidereal-timeindicating means for indicating the correction to be applied to Polaris for obtaining true altitude. Shaft 32 has integral therewith a gear 33 adapted to mesh with gear 34 integral with shaft 35. Also integral with -shaft 35 is a vgear 36 adapted to mesh with gear 31. Gear31 is rigidly attached at one end to shaft 38. The other end of shaft 38 is provided with a worm gear 38 adapted to mesh with and operate gear 4U carrying indicating pointer 4I. Since the correction to be applied to the altitude reading of Polaris to obtain correct latitude varies from zero to plus or minus sixty-one minutes, the arrangement of gears 33, 34, 3G, and 37 is such as to indicate the proper correction forA any particular sidereal time indicated.

When navigating'by dead reckoning and it is desired to check position, therdevice is used for determining which stars must be observed in order to use the precomputed curves. In the use of the device for this purpose, with counters l and 2 in their proper adjusted relationship for the day of observation, Greenwich civil time is applied to counter I and thereby converted into sidereal time on counter 2. Counter 2 will lndicate Greenwich sidereal time if longitude counter 3 is set at zero. The longitude obtained braically subtracted from the Greenwich sldereal 'time indicated on counter 2. The resulting indication on'counter 2 is local sidereal time. Using this local sidereal time in connection with Star Altitude Curves, the stars which must be used in connection with the book are determined. The altitudes of these stars are then actually observed, local sidereal time obtained from Star Altitude Curves, Greenwich civil time of observation applied to counter I and thereby converted into Greenwich sidereal time indicated on counter 2, after these counters have been properly coordinated and counter 2 actuated until local sidereal time as obtained from the book on lines of position appears thereon. The longitude of the position is then indicated in units of arc on indicator 3. Y

Referring tothe adaptation of the invention illustrated ln Figure 2, the device is adapted to be operatively connected in series with a wellknown arrangement of a constant speed motor operatively connected to drive an equatorialiy mounted telescope (not shown), about its polar axis. Such an arrangement is' illustrated on a mechanism eratively connected to ter 2a are operatively -units into units of arc.

integral with ring gear II Pages 49, 50, and 51'of General Astronomy by Young. published by Ginn and Co., Boston, Mass. By means of the diillerential gearing, the telescope may be trained on a selected star without `f disturbing the operation oi the constant speed motor and its operative connection with the indicating mechanism.

lReferring to Figure 2, constant speed motor Ia is. drivingly connected to one end of shaft Ia. Integral with the other end of shaft Ia is a gear 6a adapted to drivingly mesh with gear 1a. Gear 'la is fastened to shaft Ia, which in turn is op- Greenwich civil time counter la. Counter la and sidereal time counconnected in predetermined ratio relationship by a train of gears and shafts corresponding to those illustrated in Figure 1. These elements comprise shaft Ia, clutch elements 9a and VIIa, shaft IIa.' gears IIa and IIa, shaft IIa, gears Ila and IIa, shaft I Ia, pinion gear 22a, spider gears Ila and IIa, casing 21a., ring gear 20a, gear Ila, and shaft 32a. Clutch element Na is connected to shaft lla by pin 42a and slot IIa, as described in connection with the corresponding structure in ure 1. Longitude indicator Ia is operatively connected to sidereal-time indicator 2a by shaft Ila, gears ZIa and 21a, shaft IIa, pinion gear Ila, spider gears 24a and "a, Vhousing Zia, ring gear 20a, gear Ila, and shaft Ila. This gearing arrangement is so selected as to convert time Shaft IIa is provided with a handle 28a for manual operation to convert sidereal time to longitude. All of the elements vso far described in connection with Figure 2 are identical with those in exception of the constant speed motor Ia. peratively connected to counter 2a and shaft 32a is a shaft II having a gear Il thereon adapted to mesh with spider gears I2 and Il, freely rotatably carried by housing II. Housing II is and rotatable with respect to shafts II and Il. Ring gear II is adapted to mesh with gear Il integral with shaft II, which in turn drives local hour angle counter mechanism II. The ratio of gears II to I1 is one to two to counteract the effect of the differential gearing arrangement and enable shafts II and II to rotate at the same speed. operatively connected to shaft II to be driventhereby is a shaft II adapted to be drivingly connected to a telescope -(not shown) equatorially mounted to rotate about its polar axis at the rate of one degree per rotation of shaft II. Shaft Il, having a pinion gear I4 integral therewith adapted to mesh with spider gears It and II, is operatively connected with Right Ascension counter mechanism II. Counter II is Fis- Figure 1 with the'V adapted to be driven by manually operable handle II through shaft II and gear II in egral therewith. Gear II drivingly meshes with gear I2 integral with shaft Ii.

In the operation of .this embodiment of the invention, a civil time constant speed motor Ia drives shaft Ia at the rate of one revolution per civil minute.- Greenwich civil time is continuously indicated on counter la, sidereal time on counter 2a, and local hour angle cn counter Ii. Shaft II will be driven so that the telescopetraining mechanism driven thereby will follow the celestial body, if of constant right ascension, across the sky in the hour angle Without further attention or resetting,

If it is desired to direct the telescope to another celestial body, the telescope may be retrained, and a new right ascensicn value and hour angle value applied to counter mechanisms II` and II respectively by means of crank II without disturbing the setting on the other counter mechanisms oi the civil and sidereal time readings. This described operation constitutes the functions of this embodiment ofthe invention, which are in addition to the functions of the first described embodiment of the invention.

Obviously, if this embodiment `of the invention were to be used in a permanent location, longitude counter Ia and the gearing driving the same could be eliminated.

We claim:

An instrument for determining longitude from Greenwich civil time and local sielereal time, comprising a iirst counter for indicating Greenwich civil time, inputimeans for operating said rst counter, a second counter for indicating sidereal time, gear means including a diiferential for drivingly connecting said two counters in a civil time to sidereal time, indicating longitude, input means for operating said third counter, gear means including said differential for independently drivingly connecting said second and third mentioned counters in a ratio relationship of sidereai time to longitude, whereby operation of said inputv means for said first counter to indicate thereon Greenwich civil time obtained from a chronometer results in an indication on said second counter of the corresponding Greenwich sidereal time, and operation of said input means fo:` said third counter to change the on said second counter from Greenwich sidereal time to local sidereal time obtained from astronomical observations, results in an indication of local longitude on said third counter.

THOMAS L. THURLOW. um M. BURKA. 

